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A&A 442, 567-578 (2005)
DOI: 10.1051/0004-6361:20042476
Gravitational-darkening of Altair from interferometry
A. Domiciano de Souza1, P. Kervella2, S. Jankov3, 4, F. Vakili3, N. Ohishi5, T. E. Nordgren6 and L. Abe51 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: adomicia@mpifr-bonn.mpg.de
2 LESIA, UMR 8109, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France
3 Lab. Univ. d'Astrophysique de Nice (LUAN), UMR 6525, UNSA, Parc Valrose, 06108 Nice Cedex 02, France
4 Astronomical Observatory Belgrade, MNTRS 1940, Volgina 7, 11050 Beograd, Serbia and Montenegro
5 National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
6 Department of Physics, University of Redlands, 1200 East Colton Avenue, Redlands, CA 92373, USA
(Received 3 December 2004 / Accepted 13 June 2005)
Abstract
Interferometric observations have revealed that the
rapid rotator Altair is a flattened star with a non-centrally
symmetric intensity distribution. In this work we perform for the
first time a physically consistent analysis of all interferometric
data available so far, corresponding to three different
interferometers operating in several spectral bands. These
observations include new data (squared visibilities in the H and K bands from VLTI-VINCI) as well as previously published data
(squared visibilities in the K band from PTI and squared
visibilities, triple amplitudes, and closure phases in the visible
between 520 nm and 850 nm from NPOI). To analyze these data we
perform a 
minimization using an interferometry-oriented
model for fast rotators, which includes Roche approximation,
limb-darkening, and von Zeipel-like gravity-darkening. Thanks to
the rich interferometric data set available and to this physical
model, the main uniqueness problems were avoided. As a result, we
show that the observations can only be explained if Altair has a
gravity-darkening compatible with the expected value for hot
stars, i.e., the von Zeipel effect (
).
Key words: techniques: high angular resolution -- techniques: interferometric -- methods: data analysis -- stars: rotation -- stars: individual: Altair
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